[10.02] Dynamical Evolution of Meteoroids via the Yarkovsky Effect

The Yarkovsky effect, a radiation force produced by the
anisotropic reradiation of sunlight, causes 0.1-10 m bodies
to undergo semimajor axis, eccentricity, and inclination
changes as a function of their spin, orbit, size, and
material properties. Accordingly, it may play an important
role in delivering meteoroids to main belt resonances (and
hence to Earth). To check this, we formulated two variants
of the Yarkovsky force: ``diurnal'' (dependent on the body's
spin rate and longitudinal temperature distribution) and
``seasonal'' (dependent on the body's mean motion around the
Sun and its latitudinal temperature distribution) and
included them into a symplectic N-body integration routine
(RMVS3). Tests of our code against known benchmarks
(Rubincam 1998; Farinella et al. 1998) show excellent
agreement with their semimajor axis drift rates (+/-
0.01-0.001 AU/Myr for meter-sized basaltic objects).

We have used this code to test whether the Yarkovsky effect
delivers meteoroids to the 3:1 and/or v6 resonances
slowly enough to explain the cosmic-ray-exposure (CRE) ages
of stony and iron meteorites (~10-50 Myr and ~ 1 Gyr,
respectively). Note that an object's dynamical lifetime
after entering these resonance is typically 2-3 Myr. To
demonstrate how the Yarkovsky effect works, we will present
movies showing that stony bodies, started from a variety of
locations in the inner main belt, spiral into a resonance
within a few tens of Myr (consistent with CRE data). Thus,
since nearly any inner main belt body can produce
meteorites, we can no longer say whether large asteroids,
with huge collision cross sections, or small asteroids,
which lose nearly all ejecta during collisions, dominate the
flux of meteoroids reaching Earth. In addition, we find that
iron meteoroids, with different thermal properties, evolve
slowly enough to match CRE data. Yarkovsky forces also cause
some small bodies to undergo significant inclination
changes, which may provide an alternate escape route.